Altitude compensating heating system



March 4, 1941. H. J. DE. N. MQCOLLUM 416,935

yALTITUDE ColmrimsmING;l HEATING SYSTEM Filed Aug".y 27', 1942 .Hill

' -2 sheets-sheet 1 v March 4, 1947. H. J. DE N. MccoLLUM 2,416,935. y

ALTITUDE COMPENSATING HEATING SYSTEM I X Fled Aug. 27,'1942 2Sheets-Sheet 2 Patented Mar. 4, i947 .unirse STATI-:s PATENT OFFICEALTITUDE COMPENS SYSTE ITlNG HEATING Henry J. De N. McCollum, Chicago,Ill.; Thelma McCollum executrix oi' said Henry J. De N.

McCollum,

deceased,

assignor to Stewart- Warner Corporation, Chicago, Ill., a corporation ofVirginia Application August 27, 1942, serial No. 456,335

s claims. (ci. 15s-'28) The present invention relates .to altitudecompensating heating systems. vMore speciflcally, it relates to a novelheating system of the internal combustion type particularly adapted foruse 'in where the heat is exchanged to a fresh air stream.

The products of combustion eventually pass through an exhaust conduittoa position outside the aircraft, while the heated fresh air flows fromthe heating system to the compartments within the aircraft intended tobe heated.

The principal object of the present invention is to provide an internalcombustion heating system of the above outlined general type which hasnovel means for automatically adapting the heater to operate efficientlyat different altitudes. Yet another object of the present invention isto provide a novel heatingsystem of the internal combustion type whichis automatically adapted to operate at dierent atmospheric pressures.Another object of the present invention is to provide a novel aircraftinternal combustion heater which is well adapted for operation at anyaltitude within the range of the aircraft.

Still another object of the present invention is to provide a novelinternal combustion aircraft heater automatically adapted for operationat varying altitudes, and which includes its own Fig. 4 is alongitudinal sectional view of an alternative arrangement forintroducing a liquid fuel into a slowly moving air stream.

The heating system illustrated in Fig. 1 of the drawings is intended toreceive air for its operation from vone or more rams, these rams beinglocated at the leading edge of the airplane wing or in some otherposition where they face for-- wardly against the moving air stream. Airfrom the ram or rams passes into a carburetor intake conduit I0 and intoa main heater-conduit I2. Air entering the conduit I 0 passes through aVenturi throat I4 where la combustible mixture is formed in a manner tobe described presently. From here the combustible mixture flows througha passage I8 to a heater combustion chamber I8. It enters the combustionchamber through a .plurality of radially arranged ports 2|) formed bystriking out vanes from the side walls of a cylindrical tube. Inasmuchas these vanes are inclined somewhat from a straight radial position themixture enters `the combustion chamber I8 with a swirling motion.

Within the chamber I8, combustion is initiated by an igniter 22 of thehot wire type, this igniter being electrically energized and morefullydisclosed in my co-pending application, Serial No. 447,345, filedJune 17, 1942, for Heating apparatus. As explained in that application,after c ombustion has been well started, the igniter 22 can bedeenergized and if subsequently combustion fails for any reason, thecombustible mixture will be reignited by a reigniter 24 formed of a yspirally coiled sheet of heat and corrosion re- 'carbureting system, theheater together with the the accompanying drawings. In the drawings,

in which similar characters of reference refer t0 similar partsthroughout the several views,

Fig. 1 is a somewhat diagrammatic view of a heating system embodying thepresent invention .shown in longitudinal vertical section.

Fig. 2 is a longitudinal vertical sectional view of a detail of themechanism illustrated in Fig. 1. Fig. 3 is a longitudinal verticalsectional view of an alternative altitude compensating heating system,and f,

sistant material such as Inconel, for instance. This reigniter is morefully disclosed in my copending application, Serial No. 410,039, filedSeptember 8, 1941, now Patent No. 2,396,868, issued is passed from theram, not shown but connected to the pipe I2, to the space to be heated.

A `generally cylindrical-acoustic silencer 38 is located within thespace surrounded by the annularly arranged heat exchanger fins 34, Thissilencer is comprised of a generally cylindrical container havingperforated side walls 40 which enclose a quantity of acoustic silencingmaterial 42, such as glass wool or stainless steel wool, for instance.The silencer effectively damps out Apulsations in the combustiblemixture, thereby preventing burning from taking place in surges withinthe combustion chamber. thus eliminating the phenomenon known as motorboating. 1n order to distribute the het products of combustion from thesecondary burning zone 38 to the t tubular fins 32, the end 44 of theacoustic silencer 38 facing the combustion chamber is rounded so as todistribute the moving gases smoothly outwardly. .y l

A carburetor float bowl 48 is located below the venturi I4 and receivesliquid fuel through a pipe 48. This pipe is connected to the float bowlnear its upper edge and the fuel enters the bowl through a conventionaloat valve 60, so arranged and adjusted as to keep the bowl as nearlyfull of fuel as possible.

The float bowl is closed by a cover 52 having an opening connected to aT-tting 54, one branch ofthe T being connectedfby an elbow'56 to theportion of the conduit I8 immediatelyahead of the venturi I4. The otherbranch of the T-fitting 54 is connected by a conduit 58 to one branch ofa T-tting 80 threaded through the lower surface of the float bowl 46,the other branch of the fitting 60 being connected by a conduit 62 to acarburetor jet tube 64 having a plurality of outlet jet openings 66located axially of the low zone of the venturi I4.

The end of the T-iitting 66 threaded into the bowl 46 is closedexcepting for a small orifice 6 8 which permits gasoline or other liquidfuel to iiow from the bowl 46 into the fitting 60. I The branch of theTftting 60 connected to the conduit 58 is similarly closed excepting fora small orifice l having approximately four times the area of theorifice 68. i

vThe above described carbureting system functions as follows:

A portion of the air iiowing through the conduit I0 enters the elbow 56at a high pressure point in the conduit. IThe remaining air flowsthrough the Venturi throat I4, thus producing a lowv pressure areasurrounding the jets 66. The

. pressure differential thus produced causes a ow' The fuel in itsatomized and vaporized condition is carried with the air stream throughthe conduit 62 to the jet tube 66 Where it passes through the jetopenings 66 into the air stream flowing through the venturi I4.

The above arrangement permits fuel to be introduced into the air streampassing through the venturi I4 even though the pressure differentialproduced by theventuri is comparatively small. This is because, the fuelIiows through the jet 68 by gravity as well as by whatever pressurediifermoving air. The density of the column of fuel being liftedtherefore is comparatively low.

The heating system as above described has the orifices 68 and 18 soproportioned that a mixture of the proper degree of richness will passto the combustion chamber I6 at the maximum air density under which theheateris intended to operate, that is, at sea level pressure. As theairplane climbs to higher altitudes, thev mixture as thus supplied willbecome too rich. This is because the quantity of fuel introduced attheVenturi throat is substantially unaffected by the density of the airflowing through the venturi. 'I'he quantity of oxygen in the finalmixture, however, is directly affected by the density of the air owthrough the Venturi throat and, therefore, the lower the density of theair passing through the venturi the Iricher the resulting mixmixturesupplied to the combustion chamber I8l at higher altitudes, I haveprovided the side wall of the combustion chamber in a position adjacentthe baille plate 28 with a plurality of circumferentially arrangedperforations 12. These perforations, as well as the combustion chamberI8, are surrounded by a tubular member 14 connected to a ramknot shown.Air from, the outside, therefore, flows inwardly through theperforations continuously while the airplane is in motion. Since thisair enters through the circumferentially arranged perforations 12 inaposition adjacent the baille 28, the fresh air will be intimately mixedwith the products of combustionv issuing from the combustion chamber I8,the mixture passing through the opening 26.in the baille plate 28, andinto the .secondary combustion zone 80.

At low altitudes, the mixture entering the combustion chamber I8 is ofapproximately the ideal degree of richnesg. Combustion, therefore, takesplace rapidly and is substantially completed before the mixture reachesthe fresh air which enters through the perforations 12. Combustion is,therefore, substantially unaffected by the inward flow of fresh air. Onthe other hand, athigher altitudes when the mixture entering thecombustion chamber I8 does not have sufficient oxygen completely to.burn the fuel mixed therewith, only partial combustion takes place inthe combustion chamber. I8, the mixture flowing fromthis chamberincluding a considerable quantity of unburned fuel and carbon monoxide.The fresh air entering through the perforations 12 is intimately mixedwith this partially burned mixture, thereby supplying sufdcientadditional oxygen to convert the lremaining liquid fuel and carbonmonoxide into substantially completely oxidized elements. Under thesehigh altitude conditions, burning will'take place within the secondarycombustion zone 30 and the amount of burning that takes place in thiszone will depend upon the degree of excess richness of the mixtureentering, the combustion chamber I8.

ential exists, and further by the fact thatV the fuel passing upwardlythrough the tube 62 to the jets 65 is in an atomized and vaporizedcondition The perforations 12 are properly proportioned in size andnumber so that suflicient air ows therethrough to complete thecombustion at the' maximum operating altitude of the i airplane.Sufficient air, therefore, is always present to com# plete combustionbefore the gases pass'into the become heated faster than the heat can beconducted away. The result is that occasionally heat exchangers may warpor burn vthrough under The products of combustion Aare diluted by theair entering the Jperforations 12, thus tempering the products ofcombustion issuing from the combustion chamber before they areintroduced into the heat exchanger, thereby reducing the tendency ofportions of the heat exchanger to overheat. On the other hand, at highaltitudes where the air entering the perforations 12 is used to supportcombustion, this air has no substantial tempering effect but thistempering effect is not needed inasmuch as the air entering the heatingsystem wlill be extremely cold, thereby lowering the `temperature of theheating system as a whole. In other words, a heater properly greater theflow between the `inlet and outlet passages. Since these inlet' andoutlet passages are connected to the tubes 18 and 80, the ilow throughthese tubes, and, therefore, the flow from the T-fitting 54 to the lowerT-fitting 60', will be determined by the vertical position of the valvepin 86.

Directly above the valve pin, a Sylphon bellows l 88 is supported upon ahorizontal plate 80 secured at its edges between the housing 82 and aperforated cap 82. A yoke'94 is secured to the top of the bellows 88 andhas downwardly extending arms which pass through slots 86 in the plate80. At their lower ends the downwardly extending arms of the yoke aresecured to a cross piece 98 attached to the upper end of the needlevalve pin 86.

At sea level. the air pressure communicated to the outside of theSylphon bellows 88 through the perforations in the cap 92 causes thebellows to assume such a length that the valve pin 88 is constructed tooperate without burning through at low altitudes when the air enteringthe system through the perforatons 12 is used for tempering purposes,should also .operate satisfactorily at high altitudes even though underthese conditions the air entering through the 'perfora.

tions 1,2 is used to support combustion.

In Fig. 3 of the drawings, I have shown an altitude compensatingarrangement adapted for use with a heater having no auxiliary air inletsof the type provided in the above described embodi'l ment by theperforations 12. A heater of this type, that is, one not having theauxiliary air inlets, is illustrated and described in my co-pendingapplication entitled Heating Apparatus, Serial No. 447,345, iiled June17, 1942, now Patent No. 2,403,188, issued July 2, 1946.

The carbureting arrangement shown in Fig. 3, is, with the exception ofan altitude control valve 16, essentially similar to the arrangementshownv in Fig. 2. For this reason, the same numerals are used toindicate the same elements in the two figures. rI'he induction tube l0,the venturi |4, the float bowl 46, the T-ttings 54 and 60, the orifice68, and the jet tube 64, may all be considered as identical with thesimilar elements in Fig. 2. In Fig. 2, a passage 58 is shown asconnecting the T-fitting 54 with theA T-fitting 60, so that air from ahigh pressure point Within the induction tube I0 can be mixed withthevfuel passing through the port 68. shown in Fig. 3, the T-tting 54 isconnected by a tube 18 to the inlet side of the altitude control valve16, while the outlet side of this altitude control valve is connected toa vconduit 80 leading to the lowerT-fitting 60. Thus, air passed from ahigh pressure point within the induction tube |0 to the lower T-fittingv60 must flow through the automatic altitude control valve 16.

This automatic control valve is composed of a l housing 82 having inletand outlet passages com- In the embodiment y positioned off its seat 84the proper 'distance to permit the appropriate amount of air to iiowthrough the tube 1.8, valve 16, and tube to the T-tting 60, to form theproper heater mixture when the heater is operating under sea levelconditions. As the airplane rises,the pressureimposed upon the outersurface of the Sylphon bellows 88 will be less than at sea level.Consequently, the bellows will expand, thereby lifting the needle valve86 somewhat. This permits a more rapid flow of air through the tube 18,valve 16, and tube 80 to the T-tting 60. This, in turn, reduces thepressure differential between the T-tting 60 and the upper surface ofthe fuel within the bowl 46. The decrease in this pressure differentialdecreases the rate of fuel flow through the orifice 68 and thus a lessquantity of fuel is V carried upwardly to the jet tube 64, therebyreducing the richness of the mixture supplied to the heater. K

The above described control Valve, it will be seen, operates to reducethe richness ofthe mixture as the airplane flies into more rarefied airconditions, thereby insuring that the heater at all times, under allaltitude conditions, receives the proper mixture for, efdcientoperation. l

In Fig.' 4, I have shown an arrangement for introducing fuel into amoving air stream, 'such as the air stream through thecarburetorinduction tube I0, when the rate of air iioW therethrough is extremelylow. 'I'his arrangement comprises a comparatively large diameter Venturithroat |00 through which the air is caused to ow, thus producing a lowpressure area at the narrowest point within the throat. A second venturi|02 is arranged with its outlet-end at the low pressure area within thethroat of theiventuri |00, thereby causing the air leaving the Venturitube |02 to be at substantially the same pressure as the air within thelow pressure point of the venturi |00. IA third Venturi tube |04 isarranged with its outlet end I 06 located at the low pressure point |08of the Venturi tube |02,

4 aeiaeee throat, the annular space H2 being connected by a tube ||6tothe fuel source.

A portion of the air flowing through the induction tube passes throughthe throat of the forward venturi |00, this portion of the air beingaspirated into the throat of 'the second venturi |02, which, in turn, isaspirated into the third venturi |08. The three stagesvof pressure-droptherefore produce a low pressure area, within the throat ofthe venturi|04 sumcient to feed fuel to the air stream flowing through the deviceunder extremely adverse conditions. It will be appreciated thatalthough'in this embodiment of the invention I have shown an'arrangement of three Venturi tubes to produce a three-stage pressuredrop, it may be advisable under-some conditions to provide a four-stagepressure drop,`

while under less adverse conditions, a two-stage drop may be suiiicient.

From the above description of preferred embodiments of my invention, itwill be seen that a heating system incorporating the presentA inventionis well adapted to operate under varying air pressure conditions and,-further,- that Asuch a heating system fulfills all of the objectivesset' forth for the invention in an earlier portion of thisspecification. l

VWhile I have shown and described particular embodiments of myinvention, it will be apparent to those skilled in the art that numerousmodifications and variations may be made Without departing fromtheunderlying principles of the forming a passage connecting saidcarbureting means with the combustion. chamber and discharging ysaidmixture into said chamber, means associated with the combustion chambermeans for igniting said combustible mixture therein,

heat exchanger, conduit means connecting the combustion chamber with theheat exchanger to conduct the products of combustion to saidheatexchanger'and providing a secondary combustion zone between the chamberand said heatV exchanger, a tubular jacket around the combusv 2. Analtitude compensating internal combus-A tion aircraft heater comprisingcombustion chamber means, carbureting means separate from the combustionchamber adapted to form a combustible mixture of a liquid fuel and airwhich will burn eiciently at sea level atmospheric pressure, meansforming a passage connecting said carlouretingmeansl with the combustionand discharging said mixture into said chamber, means associated withthe combustion chamber means for igniting said combustible mixturetherein, `a heat exchanger, conduit means connecting the combustionchamber withthe heat exchanger to conduct the products of combustion tosaid heat exchanger and providing a secondary combustion zone betweenthe chamber and said heat exchanger, means introducing additional airinto the combustion chamber at the connection between said chamber andsaid conduit means for cooling the products of combustion at sea levelatmospheric pressure and for providing supplemental'air to completecombustion of the mixture in the secondary combustion' 3. An altitudecompensating internal combustion aircraft heater comprising meansforming a cylindrical combustionv chamber, carbureting means separatefrom the combustion chamber adapted to form a combustible mixture of aliquid fuel andv air, means forming a passage connecting saidcarbureting means with the combustion chamber and discharging saidmixture into "said chamber, said passage terminating within said chamberand axially thereof adjacent one end and having lateral outlets withinclined bafflesv Which'initiate a whirling motion of the mixturedischarged into the chamber, means adjacent said end of the combustionchamber for igniting said combustible mixture therein, an annular bailleplate'at the opposite end of the combustion chamber providing a centralopening for the ow of the products of combustion and any unburned gasesfrom said chamber, a heat exchanger, conduit Vmeans extending from saidbaffie to the heat exchanger to conduct said products of combustion andother'gases to the heat exchanger and providing a secondary combustionzone between thechamber and said heat exchanger, the portion of thecylindrical wall of the combustion chamber adjoining -said baiiie platehaving ports therethrough, and means to' feed air through said portsover the surface of said plate toward its central opening for admixturewith the gases flowing through said opening into the secondarycombustionzone.

- HENRY J. DE N. MCCIOLLUM. REFERENCES CITED The following referencesare of record in the le of this patent:v

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